The present invention is directed to a method for compensating tail ends of rolling materials in continuous rolling operation of shaped steel sections.
In the use of steel mills for rolling steel material it is frequently necessary to exercise careful control of the operation to avoid errors in the material being rolled. For example, when rolling tubular material, the material is stretched as it is rolled and the thickness of the wall is reduced as the tubular material passes through the various roll stands. The reduction in thickness is accomplished by applying a tension to the tubular material as it passes through the roll stands. This tension is generally applied by having the speed of successive roll stands operate at a speed greater than that of the preceding roll stands. However, the tension thereby produced does not only occur between two successive roll stands but, as the tubular material passes a particular roll stand all of the previous roll stands exert a retarding force to increase the tension on the tubular material. Because of the tension operating condition, the tail end of the tubular material is generally thicker than a central part of the tubular material, because the tail end of the tubular material does not have the retarding force by the preceding roll stands.
A solution to this problem for tubular materials in suggested in U.S. Pat. No. 3,645,121 which provides an increased amount of tension on the end portion of the tubular material in a stepwise variation of the rolling speeds of the roll stand, to thereby introduce a stepwise graded tension increase onto the end portion of the tubular material. This patent increases the tension by sequentially modifying the speeds of successive roll stands in accordance with a predetermined pattern whereby only the tension in the end portion will be increased without affecting the central portion of the tubular material.
While such techniques are known with regard to rolling of tubular material, a completely different problem exists when rolling shaped steel sections such as H shaped steel sections. In such type of rolling operation, the tension between roll stands is zero during normal rolling. Therefore, the rolling operation itself does not introduce any irregularities in the rolling material. However, the shaped steel sections normally has flanges at its edges. At the end portion of rolling material for such flanged shaped steel sections there is a crop which is cropped and has a deformity and irregularity wherein the flanges are generally lacking at the tail end. In rolling such shaped steel sections, a roll stand is usually provided two sets of rollers in the continuous rolling, namely a vertical set and a horizontal set. As the crop at the tail end enters a particular roll stand, while the horizontal rollers are held in contact with the flat or horizontal section of the rolling material, the vertical rollers which normally engage the flanged edges, are now freed from any rolling load. The result is that there is a reduced amount of contact between the rollers of this particular roll stand rolling the crop compared with the succeeding roll stand which encounters both a vertical and horizontal section. The result is that the tail end of the rolling material between the particular roll stand and the succeeding roll stand is overfed into the succeeding roll stand and there occurs defects in the shape of the rolled material. The compressive force between these two roll stands tends to form a bump or irregularity in the rolled material.